1. Field of the Invention
This invention relates generally to apparatus and methods for radar impact detectors, and especially to systems which are used to deploy a side air bag in advance of an imminent side vehicle collision.
According to a report by Ludo Careme of the Belgian Insurance Group, side impacts are second in lethality to head-on collisions, accounting for about 30% of the total numbers of serious automobile related injuries in European countries. More than half of all side impacts occur in intersection collisions in which the cars are traveling on paths perpendicular to one another. The most dangerous impacts are those in which the car is struck centrally. When the collision is off-axis, much of the impact energy is transferred into less damaging rotations of the impacted vehicle.
In response to the above dangers, automobile manufacturers are now beginning to install side airbags. One luxury class car maker now advertises that since 33% of all car accidents are side-impacted collisions, they have installed front seat-mounted, side-impact airbags for both driver and passenger in their 1997 model. However, traditional accelerometer or acoustical based switches must wait for impact to initiate, which, because of the proximity of the passenger to the impact area, limits passenger protection capability. The rapid inflation requirement imposed by post-impact initiation also increases the risk of passenger injury due to airbag deployment alone, with many deaths per year now being attributed to airbag deployment in the less strenuous front airbag scenario. Automobile manufacturers are now searching for a predictive triggering system to initiate the inflation of side airbags a minimum of 15 to 20 milliseconds prior to impact.
2. Background Art
Systems and devices for collision avoidance of air, sea, and ground vehicles are in general well known. Early devices utilized forward-looking antennae with radio frequency transmitters and receivers. In U.S. Pat. No. 3,891,966, Sytankay disclosed a laser system designed to avoid rear end collisions between automobiles. This apparatus provides a laser transmitting and receiving system and a detection system mounted on the front and rear of automobiles. The transmitter at the front end emits a signal having a designated wavelength f.sub.1 and the receiver at the front end receives signals having a designated wavelength f.sub.2. Upon reception of signals of wavelength f.sub.1, the modulator at the rear end of a leading car would activate the transmitter which would send a return signal of wavelength f.sub.2 to the receiver at the front end of the trailing car. This signal is interpreted by circuits in the receiver and furnishes a warning of the proximity of the vehicles.
Sterzer, et al, in U.S. Pat. No. 4,003,049 shows a frequency-modulated continuous-wave collision avoidance radar responsive to both reply signals from cooperating (tagged) targets and to skin reflections from proximate non-cooperating (non-tagged) targets.
German Patent No. 2,327,186 and U.S. Pat. No. 4,101,888 to Heller, et al, describe a system in which detections are limited to the "electronic road channel" in which the vehicle is traveling. The radar has two antennas which radiate RF signals of different frequencies. The signals received by one of the two antennas are evaluated by determining the difference between the amplitudes of the RF signals reflected from an object. A signal proportional to the difference is then compared to a threshold proportional to a predetermined azimuth range, so that cars moving in the same road lane may by discriminated against other passing objects.
More recent devices employ a millimeter wave antenna capable of electronic scanning. An example is shown in U.S. Pat. No. 5,264,859 to Lee et al, in which a linear ferrite loaded slot array illuminates a dielectric lens. Beam scanning is achieved by controlling a bias magnetic field along the ferrite rod of the slot array. More advanced systems might employ a conformal array disposed within or around car structures such as bumpers. Such antenna systems are generally taught by Speciale in U.S. Pat. No. 5,512,906.
A more complete total avoidance system is discussed by Shaw et al in U.S. Pat. No. 5,314,037. Here, the laser detection system is coupled to both warning and automatic car control devises, such as steering and braking systems, in order to take evasive action. Obviously, such complex systems are expensive to build and will have a lower inherent reliability. Although the above systems may find utility in avoiding front and rear collisions, they are not adapted for early warning of imminent side collisions.